<template>
    <ul class="list">
    <li
      class="item"
      v-for="item of letters"
      :key="item"
      :ref="item"
      @touchstart.prevent="handleTouchStart"
      @touchmove="handleTouchMove"
      @touchend="handleTouchEnd"
      @click="handleLetterClick"
    >
      {{item}}
    </li>
  </ul>
</template>

<script>
export default {
    name:'CityAlphabet',
    props:{
        cities:Object
    },
    data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
    updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
    computed: {
      letters () {
        const letters = []
        for (let i in this.cities) {
          letters.push(i)
        }
        return letters
      }
  },
    methods:{
        handleLetterClick(e){
             this.$emit('change', e.target.innerText)
        },
        handleTouchStart () {
             this.touchStatus = true
        },
        handleTouchMove (e) {
          if (this.touchStatus) {
            if (this.timer) {
              clearTimeout(this.timer)
            }
            this.timer = setTimeout(() => {
              const touchY = e.touches[0].clientY - 79
              const index = Math.floor((touchY - this.startY) / 20)
              if (index >= 0 && index < this.letters.length) {
                this.$emit('change', this.letters[index])
              }
            }, 16)
          }
        },
        handleTouchEnd () {
          this.touchStatus = false
        }
    }

}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
</style>
